The invention relates to a method for the electro-dipcoating of electrically conductive elements, such as screws, nuts, shims or other hardware, the elements, which are to be coated, being positioned in, on or at a supporting element in a coating bath, which is provided with at least one anode and one cathode.
Different procedures are known for electro-dipcoating or electrophoretic enameling. Frequently, the metallic supporting elements must be cleaned after the treatment, so that an electrically conducting, active, metallic surface is exposed once again. A series of disadvantages are associated with this. In particular, large amounts of electrophoretic enamel, which may be regarded as a valuable material, are wasted. The cleaning, which is usually carried out with solvents, is comparatively costly and expensive and, moreover, time-consuming, especially when it is carried out sealed off from the environment.
It is therefore an object of the invention to provide a solution, with which electro-dipcoating can be carried out with anodes and cathodes and supporting elements which, after taking up electrophoretic enamel for a firsttime, can be used further without a prior cleaning and without taking up electrophoretic enamel once again after the subsequent, repeated use.
This objective is accomplished with a method of the type described above owing to the fact that, in the case of a cathodic electrophoretic enameling, the anode and, in the case of an anodic electrophoretic enameling, the cathode is coated with an enamel, which was baked after the coating process and subsequently activated and/or coated with an electrically conductive enamel, which was subsequently cured at room temperature.
The advantage of the present invention lies therein that the anode and the cathode are activated with an electrophoretic enamel in such a manner, that they are subsequently conductive equally well for DC as well as for AC currents of different voltages.
In a development, the anode and cathode and/or the supporting element are coated with a cathodic or anodic electrophoretic enamel with a voltage, until the current no longer flows. Subsequently, the enamel is baked or cured at room temperature and, after that, the coating of the objects is activated by applying a DC or AC voltage. In a further development, the supporting element, after it is coated with electrophoretic enamel, is equipped with the object that is to be coated, brought into the eletrophoretic enamel and, while the object is being coated, exposed to a few high current surges, especially dc current surges, for the activation.
It is advantageous if, as is also provided for in the invention, the electrophoretic or coating enamels contain a proportion of electrically conducting materials, such as graphite or a metal.
Corrosion protection can also be provided pursuant to the invention. Such a method is distinguished owing to the fact that the anodes or cathodes, before the enameling or the electro-dipcoating and the subsequent activation of the coating, previously are coated first with a material providing corrosion protection, such as a zinc dust paint.
Pursuant to the invention, it is possible to operate the anodes or cathodes, depending on the procedure, freely in the coating basin, that is, outside of a dialysis cell, although the invention alternatively also provides for the use of such a cell.
Aside from conventional, known metallic anodes and cathodes and also metallic supporting elements, these elements can also be constructed pursuant to the invention as plastic elements, which are provided with metallic coatings before the electro-dipcoating and then are used in the inventive method.
It has turned out to be particularly advantageous to carry out the coating process at 20 to 500 V dc and to carry out the activation with current surges of up to 1,000 V. A drum or a basket can be used as supporting element for bulk material or a frame for suspending articles that are to be coated.
In order to make continuous processing feasible, it is also possible to use a coating belt, which has been enameled and activated according to the inventive procedure.
Advisably, the supporting elements for the activation can be provided with very densely packed electrically conductive objects, as is also provided for in a further development of the invention.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to is construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.